The semiconductor device industry has experienced rapid growth. In the course of semiconductor device evolution, the functional density has generally increased while feature size has decreased. This scaling down process generally provides benefits by increasing production efficiency and lowering associated costs. Such scaling down has also increased the complexity of design and manufacturing these devices.
One technique applied to the design and manufacturing of semiconductor devices is optical proximity correction (OPC). OPC includes applying features that will alter the photomask design of the layout of the semiconductor device in order to compensate for distortions caused by diffraction of radiation and the chemical process of photo-resist that occur during the use of the lithography tools. Thus, OPC provides for producing circuit patterns on a substrate that more closely conform to a semiconductor device designer's (e.g., integrated circuit (IC) designer) layout for the device. OPC includes all resolution enhancement techniques performed with a reticle or photomask including, for example, adding sub-resolution features to the photomask that interact with the original patterns in the physical design, adding features to the original patterns such as “serifs,” adding jogs to features in the original pattern, modifying main feature pattern shapes or edges, and other enhancements. As process nodes shrink, OPC processes and the resultant patterns become more complex.
One type of advanced OPC involves inverse lithography technology (ILT). ILT includes simulating the optical lithography process in the reverse direction, using the desired pattern on the substrate as an input to the simulations. The ILT process may produce complex, curvilinear patterns on a photomask or reticle, rather than the Manhattan patterns that are formed on conventional photomasks or reticles. Unfortunately, conventional ILT photomasks and the methods of fabrication thereof still face various difficulties with respect to the non-Manhattan patterns.
Therefore, although existing ILT photomasks have been generally adequate for their intended purposes, they have not been entirely satisfactory in all respects, in particular the missing of an accurate mask model capable of dealing with non-Manhattan patterns.